FR2697713A1 - Support for microwave heating of foodstuffs in metallic containers - comprises partially soaked sponge material which converts part of microwave energy into heat transferred by conduction, convection or condensn. - Google Patents

Abstract

Appts. for heating prod. in microwave ovens consists of a support (1), formed from spongy squeezable material, soaked with a liq. which absorbs microwave energy and partially wrung out, which diverts a large proportion of the electromagnetic energy, and converts it into heat transferable by conduction, convection or condensn., to the contiguous prod.. USE/ADVANTAGE - Cooking of prods. in metallic containers and plastic sachets. Combination of traditional and microwave heating. More homogeneous temp. than microwave heating. Support is easy to handle immediately after cooking. Used for wide range of containers.

Description

 Device for heating products in a microwave oven with a spongy support soaked, and means for its implementation.

 The invention relates to a microwave heating device, which converts a large fraction of the electromagnetic energy into thermal energy, transferable by conduction, convection, condensation to a contiguous product.

 This invention finds application more particularly for the heating of food products, with the aim of raising them quickly and safely, in their primary packaging, to the usual consumption temperature, with improved temperature uniformity.

 An advantageous application lies in the heating of food products containing metal, tray or box.

 Another interesting application relates to the heating of food products containing flexible.

 The widespread use of microwave speakers, called microwave ovens, is a reflection of their convenience of use. The electromagnetic energy, called microwave, available in the cavity of the apparatus, at the authorized frequencies, is transformed into heat energy or heat in all absorbing substances present, in a proportion function in particular the dielectric characteristics of these substances. In a food product, the water of composition and the mineral salts play a preponderant role, and allow a supply of energy such that the average temperature of usual consumption is reached in a few minutes. Some so-called combined speakers also provide energy. in other forms: infrared or ambient heat more or less ventilated: These particular constraints are attached to them concerning the packaging materials usable according to their own resistance to the temperature.

 However, several phenomena limit the convenience of use and concern the safety and temperature distribution, both for fresh products, refrigerated canned canned or, more critically, frozen.

Safety and temperature distribution can be related:
For example, risk of overheating projections at certain points,
risk to health, because of an insufficient time-temperature scale for the
destruction of microorganisms and harmful substances at certain points,
or the excess of advancement of natural chemical reactions in others.

Safety and temperature distribution can also be independent:
Safe handling of hot products, safety for equipment
microwaves, security against the explosion of leakproof packaging
with water vapor; Temperature distribution too heterogeneous for a
usual organoleptic satisfaction (eg uncooked fish) or
leading to excessive drying (eg hard crust not consumable)
The metal containers and containers combine the inconveniences, but nevertheless have many advantages: Rigidity, cost, thermal conductivity, resistance to infrared radiation, better controlled recyclability, thermal stability of the most negative temperatures up to 400 ° C, gas tightness.

Also, many development works have addressed this problem:
For example, EP 0 299 237 discloses a plastic cover or sealed cardboard, constituting a receptacle for an absorbent fluid. The important unit cost (estimated at 2 times the cost of the metal tray), the risk of handling the lid somewhat stiff and filled with boiling water, the specificity of the lid to the tray limit the interest of the device.

 United States Patent 4,439,656 illustrates a utensil made of a material transparent to microwaves, in which a metal tray is placed and which once filled with water in the small space between wall and tray, allows the reconstitution of frozen products. This device is specific to a single size and conformation tray, otherwise difficult to extract after heating. He calls for a precise adjustment of the amount of water added.

 EP 0 364 402 relates to a device to hang or snap on the edges of an electrically conductive container to avoid the risk of arcing, by spacing with the walls of the microwave oven. This device does not provide a solution to the temperature heterogeneity and does not eliminate the risk of electrical contact between the bottom of the tray and, for example, a metal support grid, as found in combi ovens.

 French Patent No. 2,565 (9,565) relates to a packaging, a heat-resistant plastic bag, wrapped in a metal tray.This packaging regulates the risk for the microwave equipment but does not allow the grating by infrared, and does not bring improvement of heterogeneous temperatures.

 EP 0 334 772 discloses a heating process in a microwave oven having a wall interposed between the generator and the useful chamber. The porous wall, capable of water retention, is, in operation, the seat of an intense vaporization which transforms the microwave oven into a vapor containment furnace. The apparatus is totally dependent on the type of microwave enclosure and the configuration of the waveguide (s) directing energy to the cavity. If the device avoids excessive drying, its main objective is to create a heterogeneity of temperature to preserve the cooking qualities of food, as they result from cooking other than microwave.

 A large proportion of industrial ready meals are offered in sealed plastic bags, usually of a complex material based on polyamide, polypropylene, polyester and polyethylene. Originally intended for heating by water bath, these products are suitable for the microwave oven, with, however, the disadvantages mentioned above and, more particularly, the risk of explosion of the bag when the partial pressure of the steam water generated by overheated dots, mainly in the corners, exceeds the resistance of the material or welds. Manufacturers recommend piercing the bag before submitting it to the microwaves; this creates significant handling difficulties after reheating, with product leaks.

 The present invention overcomes these multiple disadvantages. It is based on the particular properties of heat dissipation of the microwave energy in a sponge material wringing, soaked with an absorbent liquid, and partially wrung out. This assembly, consisting of the spongy material and the absorbent liquid dispersed therein, placed near a product of dielectric characteristics similar to the liquid, preferably absorbs the microwave energy. This complex entertains a large fraction of the available electromagnetic energy, and converts it into transferable heat by conduction, convection or even condensation if the temperature reached by the spongy assembly allows the vaporization of a composition element of the assembly.

 The invention consists in using, inside the microwave oven, this spongy assembly as a support for the product, advantageously in its packaging and placed contiguously or overlying, or inside a cavity.

 The spongy material is characterized by a structure of organization of the largely porous material, elastic in the impregnated state, made of fibers or veils of fibers and / or interconnected pores, and adapted to imbibe by capillarity, thanks to the fine of their network. the natural sponge, horny demosponge, belonging to the genera Hippospongia and Euspongia, is the illustration of this structure. The material is preferably regenerated cellulose, scleroprotein, polyethylene or polybutylene terephthalate, polyolefin, for example high density polyethylene, polybutylene, polymethylpentene, polypropylene, polyetherimide, polystyrene, polychloro vinyl, polycarbonate or suitable combinations of these materials and their monomers.

 The bulk density of the unimpregnated and uncompressed sponge material is preferably between 5 and 150 kilograms per cubic meter (Kg / m 3), optionally between 15 and 80 Kg / m 3 if the material is regenerated cellulose from viscose obtained by treatment of alkalicellulose with carbon disulfide, if appropriate.

 The microwave-absorbent imbibing liquid may be water or any absorbent substance or solution with dielectric characteristics similar to the product placed contiguously. The imbibition of the absorbent liquid, in the spongy material, before action of the microwaves, can be carried out by dipping or passing under a flow of liquid, followed, if necessary, by dewatering by pressing, twisting, blowing, suctioning, or well by dosing or spraying the necessary amount of liquid, as defined below.

The support may have a height of between 10 and 50 millimeters, preferably between 30 and 120 millimeters; Its dimensions in a horizontal plane may be a function of the type of oven and the application envisaged, and in particular to support several products at the same time,
The material of the possible packaging of the product, if the contact with the spongy material is neither desired nor possible, can be cellulosic (cardboard or paper, if necessary impregnated or plasticized), metal (aluminum, tinplate or chromium, optionally lacquered), polyolefin plastic, vinyl, styrene, polyester, polyamide), glass, ceramic, or a combination of these materials.

 In the case of sealed packaging, it will preferably remove the lid or the lid, or cut an opening on the side of the bag before use, to avoid the risk of a dangerous internal pressure at the opening. This manipulation is generally easy cold for food products whose sauce is frozen.

 In the case of metal packaging, it will advantageously remove the cap or the metal cover, if necessary, before use of the device, although it still allows otherwise to heat the product, but with limited effectiveness, close to a bain-marie heating with regard to quality and duration.

 The advantage of the device of the invention is to ensure, in a controlled manner, a mixed microwave heating and conventional thermal transfer, to improve safety and temperature distribution: Both industrial and 'general public' applications are possible.

The description which follows makes it possible to better understand the invention with reference to the drawings which illustrate preferred embodiments thereof:
In the drawings,
Figure 1 is a perspective view with a partial sectional corner
of the device, namely the spongy assembly in support of a container
rectangular base taken as an example.

Figures 2 to 7 are perspective views of various shapes,
variants of the device of FIG. 1, for heating trays
rectangular, oval, polygonal, or cylindrical boxes.

FIG. 8 is a perspective view of the device applied to
heating a flexible bag whose side placed at the top
opened.

 Figure 9 is a sectional view along AA of Figure 8.

 FIG. 10 is a variant of the device of FIG.

 Figure 11 is a sectional view along BB of Figure 10.

At drawings,
The spongy material device i, for containing and supporting a tray 2, has a cavity 3 to safely accommodate the container.

 Table 1 below summarizes the dimensional characteristics of devices according to Figure 1, for different containers and contents, and given here as non-limiting examples to illustrate the presentation.

Table l

<tb><SEP> Dimension <SEP> Dim. <SEP> External <SEP> Weight <SEP> sec <SEP> liquid <SEP> volume <SEP> of
<tb> Ref <SEP> Product <SEP> cavity <SEP> 3 <SEP> support <SEP> i <SEP> support <SEP> i <SEP> imbibed <SEP> suppart <SEP> -1
<tb><SEP> mm <SEP> mm <SEP> 9 <SEP> 4 <SEP> cm3
<tb><SEP> flat <SEP> individual
<tb><SEP> A <SEP> 250 <SEP> to <SEP> 300 <SEP> g <SEP> i00xi3tixis <SEP> 140x175x40 <SEP> 20 <SEP> 80 <SEP> 75CJ
<tb><SEP> tray <SEP> aluminum
<tb><SEP> dish <SEP> cooked <SEP> 2/3 <SEP> pers
<tb><SEP> B <SEP> 450 <SEP> to <SEP> 600 <SEP> g <SEP> i20x180xi8 <SEP> 720x230x40 <SEP> 35 <SEP> 125 <SEP> 1150
<tb><SEP> tray <SEP> aluminum
<tb><SEP> flat <SEP> family
<tb><SEP> C <SEP> 800 <SEP> g <SEP> to <SEP> 1.2 <SEP> Kg <SEP> 155x220x18 <SEP> 215x280x40 <SEP> 50 <SEQ> 170 <SEQ> 1750
<tb><SEP> tray <SEP> aluminum
<tb><SEP> D <SEP> box <SEP> retains <SEP> round <SEP> / b <SEP><SEP> 100 <SEP> x <SEP> h55 <SEP> 145x145x80 <SEP> 45 <SEP> 140 <SEP> 1250
<tb><SEP> 800 <SEP> g <SEP> approximately
<tb><SEP> E <SEP> box <SEP> retains <SEP> round <SEP> 8 <SEP> 75 <SEP> x <SEP> h55 <SEP> 120x120x80 <SEP> 30 <SEP> 120 <SEP> 900
<tb><SEP> 400 <SEP> g <SEP> approximately
<Tb>
In the embodiments according to FIGS. 2 to 7, the cavity 3 may be more or less deep, have a vertical or angled cut, with straight or rounded corners, the support may be of parallelepipedal external shape, or with rounded faces or various shapes to facilitate manipulation or gripping if desired. These examples of forms, given as an indication, do not interfere with the basic features of the invention and are therefore not limiting.

In the preferred embodiments illustrated in FIGS. 8 to 11, and characterized by the fact that the cavity 3 is inclined, the cavity is able to receive and support one (or more) sachet (s), open on the upper side
or cut beforehand. A holding function to prevent overturning is advantageously entrusted to the support and completes its thermal interest to reduce a heterogeneous temperature distribution, a risk of bursting of the bag, a risk of splashing or soiling, the inconvenience of the counteracting operation. nature of piercing a waterproof bag.

 In all of the preferred embodiments, it has been noted that after heating by microwaves of the sponge assembly, soaked slightly according to the characteristics defined below, and supporting the product thus heated, the low thermal conductivity of the Spongy set allows to enter the device, after a few seconds of the microwave stop, without risk of burns, with an impression of heat quite bearable.

The following description provides a better understanding of the invention and its ability to control the energy distribution according to the rate of imbibition or spinning of the spongy support with the absorbing liquid, with reference to the graphs of FIGS. 12 to 16.
FIG. 12 shows, by way of example, the temperature rise kinetics of a spongy assembly, composed of a synthetic sponge (cellulosic dry mass 209 - volume 465 cm3 - 125x93x40), soaked with 609 of water example of absorbing liquid. This assembly has been placed, for the example mentioned, close contactless, a high density polyethylene tub, of identical dimensions and containing 280 grams of cold water, whose kinetics of temperature rise t2 was found simultaneously, during heating in a microwave oven. A rise is noted four times faster than t2, with evaporation of the imbibition water from the point E, while the water of the container is still at an average temperature of about 30 degrees Celsius.

FIG. 13 shows, in a similar experimental device, the influence of the thickness e of the sponge assembly on the temperatures reached after one minute of microwave action in the domestic oven:
til is the temperature of a spongy set of dimensions 125x93x e mm
and soaked in 60 grams of water.

 t21 is the temperature of the water (1809) in the polyethylene tray.

t12 is the temperature of a spongy set of dimensions 125x93x e mm
and soaked in 100 grams of water.

 t22 is the water temperature 1140g) in the polyethylene tray.

It can be noted a good stability of the temperatures reached for a thickness of 40 mm and beyond. The decay of the desired effect, clearly observable in t12 at 15 mm thick, is due to the saturation S of the sponge by the absorbing liquid (100 grams of water in 200 cm3 = 8 g of dry sponge).
FIG. 14 shows, in a similar experimental device, the effect of the quantity of water, called the water load, soaking up the spongy set (125x93x40 - cellulose dry matter = 20 g), on the temperatures reached after one minute of microwave action in the microwave oven ::
tltoo is the temperature of the spongy set for a quantity of water
in the adjacent tray equal to 100 g - final temperature t2 iX
tl3 is the temperature of the spongy set for a quantity of water
in the adjacent tray equal to 300 g - final temperature t2 o
tu500 is the temperature of the spongy set for a quantity of water
in the adjacent tray equal to 500 g - final temperature t2soo
A particularly interesting effect is noted with regard to the high temperature reached between 20 and 150 grams of water load for the experimental cancellous unit, ie an imbibition of 50 to 350 grams of absorbent liquid per cubic decimetre (g / dm3). preferably between 80 and 250 g / dm3, advantageously 170 g / dm3. It is also noted that the temperature reached is not very dependent on the quantity of product associated with it.

 FIGS. 15 and 16 complete the experiment described, by way of example in FIG. 14, and show the calculated energy correspondence of the temperatures measured and reported in FIG. 14. FIG. 15 graphically reports the value D = energy bypass the spongy set = proportion of the microwave energy used, captured by the spongy set.

divided by the weight proportion of absorbing liquid on the total present in the microwave cavity. FIG. 16 gives, for the test carried out, the quantity of energy in Watts captured by the sponge assembly.

 FIGS. 15 and 16 show that the derived energy, captured by the spongy assembly, is not very dependent on the load of the associated product in proximity, and that the maximum of this energy is for an imbibition of 170 to 350 g of liquid absorbent by dm3 of spongy set.

 The cavity 3 comprises, preferably a notch 4 at the periphery of the cavity bottom, which improves the deformability of the material and, consequently, the adaptation to containers of neighboring dimensions. One possible embodiment of the cavity 3 and the notch 4 is illustrated in FIGS. 17 and 18 and the result obtained as shown in FIGS. 19, 20 and 21.

FIG. 17 shows the simultaneous cutting of the wall of the cavity 3 and the notch 4 with a suitable cutting tool, for example a jigsaw set at a depth of
FIG. 18 shows the horizontal cut and the recess of the cavity with a suitable cutting tool, possibly vibrating blade and possibly notched, after pressing the compressible sponge surround with a plate of dimensions slightly greater than the recess to achieve. This possible embodiment of the cavity 3 of depth c, does not exclude other modes such as for example the nibbling recess or the embodiment by molding, to obtain the usable support illustrated in Figure 19 showing a section of the support .

The external dimensions of the individual support product, according to the invention are preferably defined. Referring to the drawing of Figure 20, showing a longitudinal section of a support and visualizing the position of an overlying tray 2 in the cavity 3, the dimension m of the surrounding margin of the spongy support, is advantageously designed to provide, in all circumstances, between the envelope volume of the tray and the envelope volume of the cancellous support, a spacing f preferably greater than 5 millimeters, such that it prevents any possible approximation between a metal tray, used if necessary, and another conductive metal part inside the cavity. This preferred arrangement eliminates the risk of electric arc and consequent degradation of the microwave oven.It remains valid, if using a tray of significantly larger dimensions, because, with reference to Figure 21, is observed thanks to notch 4 interesting deformation of the cancellous support 1
A major advantage of the device according to the invention lies in obtaining a higher homogeneity of temperature in heating by microwaves For information, the following comparative examples illustrate the performance of the spongy support device according to the invention, with reference the graphs of Figures 22, 23, 24 and 25 which show the results of tests with (I) or without (0) a spongy support i, soaked with 80 g of cold tap water and corresponding to the reference A of the table I, supporting suitable trays, without lid, either polyester (P) or aluminum (A) and containing a mass of 350 grams of salt purée at 1So, reconstituted from flakes of earthenware, or fluid (F) at 9% dry matter, or thick (E) at 14% dry matter; for example FAI means: fluid puree in aluminum tray on the device
according to the invention.

EPO means thick puree in transparent crystallized polyester trays
microwave, WITHOUT the device according to the invention.

Figures 22 and 23 show results obtained with a content at + 6'C
Figures 24 and 25 show results with frozen initial contents
at -22 "C.

Figures 22 and 24 graphically illustrate the position of the tests according to the axes: in abscissa standard deviation calculated S defined as criterion of dispersion
temperatures in the content warmed to 55 "C average temperature
in the time T55 brought to the ordinate.

 FIGS. 23 and 25 graphically illustrate the position of the tests along the axes: on the abscissa standard deviation obtained S, on the ordinate the observed evaporation E.

 For a fresh content, it is found, in the analysis of Figures 22 and 23, that the device according to the invention allows a temperature homogeneity twice better than without device (5.5 C compared to 10.7 C J. L Evaporation E of the product leading, optionally to dryness, tough crust, burns, splashes, is reduced by the device according to the invention to one-third of the evaporation without the device.

 For an initial frozen content, it can be seen from the analysis of FIGS. 24 and 25 that the device according to the invention considerably shortens the heating time necessary to obtain 55 C when the container is a thin aluminum metal container, and even conducts in this case, the best homogeneity observed. The device according to the invention is particularly relevant and preferable in combination with metal containers.

 All containers combined, the device according to the invention allows a homogeneity of temperature, described by the standard deviation S, substantially better than without device with frozen products. The evaporation E of the product is reduced with the device to one-third of the evaporation without a device according to the invention.

Claims (6)

E VENDICAIlONS  1) Heating device in a microwave oven characterized in that it is a support (1) consisting of a spongy material essorable, soaked with a liquid absorbing microwave energy and partially wrung out to divert a significant fraction of the Electromagnetic energy converted by the device into transferable heat by conduction convection or condensation to an adjoining product.  2) Device according to claim 1 characterized in that it comprises a cavity (3) in the spongy support of respective dimensions such that no metal part of a container (2) placed in said cavity can come into contact with another metal element of the oven or other container.  3) Device according to claim 2 characterized in that a notch (4) is formed in the perimeter of the cavity bottom.  4) Device according to claim i characterized in that the support (i) is provided with a cavity (3) inclined relative to the horizontal.  5) Device according to any one of the preceding claims characterized in that the energy absorbing liquid is 1 water, the spongy material is a synthetic sponge, and that the contiguous product is a food product.  6) Device according to claim 5 characterized in that it is recommended a wicking rate of the sponge between 50 and 350 grams of water per cubic decimetre.